Method of casting metal ingots



March 17, 1953 H. E. KENNEDY 2,631,344

METHOD OF CASTING METAL INGOTS Filed on. 14, 1950 SURFACES OF 188 STAINLESS STEEL INGOTS MAGNIFIED 2 DIAMETERS CAST IN 1 CAST IRON MOLD CAST IN SILICATE SHELL IN VEN TOR.

HARRY E.KENNEDY A RNEY Patented Mar. 17, 1953 UNITED STATES PATENT OFFICE METHOD OF CASTING METAL INGOTS Application October 14, 1950, Serial No. 190,185

7 Claims.

In the fabrication of metal articles, the casting of an ingot of the appropriate metal is often a preliminary step. As is well known, the facility and cost of the subsequent operations for manufacturing bars, rods, plate, Wire and the like depend in large measure upon the quality of the ingot, and the production of the latter is a critical operation. One of the most important features of an ingot is the nature of its surface: if this is impaired by cracks, pits, occlusions or other defects, the ingot becomes unsuitable for further working, such as forging, rolling or drawing. In that case a high proportion of defective plates or other products will result, and it may be necessary to scrape the whole ingot. To secure an acceptable ingot surface it is often neces sary to remove defects by local chipping or grinding, or even to take off the entire surface by oxygen cutting or machining. The cost of such measures in labor and lost metal is often a major item in the price of the finished goods.

The problem of casting ingots having good surfaces is presented by practically all high-melting alloys, including alloy steels; and even carbon steels produce ingots with surfaces less perfect that are needed when the ingots are to be used for certain exacting purposes, such as the manufacture of seamless tubing. Considerable percentages of such alloying metals as chromium, molybdenum, nickel and vanadium often give compositions from which it is notoriously difiicult to make ingots having acceptable surfaces, Nichrome being a conspicuous example.

A principal object of the invention is to provide a process of casting workable metals and alloys to form thereon a surface substantially free from imperfections which deleteriously afiect the worked article formed therefrom. Another object is to facilitate the casting of ingots. A further object is to prolong the useful life of ingot molds. Other objects will appear as the description proceeds.

During researches carried out by the applicant in which a high-melting alloy was caused to solidify from the molten state in ingot molds lined with shells of silicate material, said material having a lower melting .point than the alloy in question, it was observed that the bodies of solid metal produced had better. surfaces than those obtainable by casting ingots of the alloy by conventional methods. Such a procedure, however, presents many difliculties and in general is not reliable or satisfactory. Due to the difference in thermal expansion between the mold walls and the silicate material constituting the shell there is a tendency for the silicate shell to spall thus leaving bare spots or areas on the ingot mold inner face. During the casting of the molten metal these bare spots lead to the development of cold shuts and other irregularities on the final ingot surface. Also the presence of bare spots or areas on the inner mold wall leaves the mold wall unprotected, and the molten metal during casting, unless the temperature is carefully controlled, may freeze upon the wall in such a manner as to produce a sticker. This situation results in surface imperfections on the ingot and also increases the time and difficulty of ingot removal from the mold. Additionally, this condition leads to excessive need for mold repair and eventual mold replacement. Another difficulty, equally serious, which is present even when there is no spalling of the silicate material is the accumulation of metal splashings in the silicate shell as the molten metal is cast. These splashings stick to the frozen silicate shell and appear as scabs and slivers on the final ingot surface.

According to the invention ingots having excellent surfaces can be made by casting refined and purified metal in shells of fusible silicate material when the shell is prepared and maintained according to the special procedures herein explained in detail. One important condition that must prevail to offset the aforementioned difliculties has to do with the temperature gradient existing throughout the silicate shell wall. It is of primary importance that the inner walls of the silicate shell, 1. e. the walls which will contact the molten metal during casting, be at a temperature in excess of the outer walls, i. e. the walls which contact the supporting envelope or mold structure. Preferably, the inner walls should be at a temperature approaching the melting point or solidus of the silicate material. When the inner walls of the shell are in this condition the shell will not spall and metal splashings occurring during the pouring operation tend to liquefy the surface of the shell at the point of impingement and thus cannot be retained on the shell inner wall. The spl-ashings fall back into the molten metal being cast and thus do not form scabs and slivers on the ingot surface. It is also of primary importance that the outer walls of the silicate shell be at a temperature sufficiently low to freeze the molten metal so that the molten metal will solidify in contact with the shell and at no point come into contact with the supporting envelope or mold structure.

The combination of silicate shell and supporting envelope may take many different forms. The supporting structure may be, for example, a metal member consisting of one piece, or a plurality of interfitting pieces; and since conventional ingot molds are readily available, and are well adapted to serve as the shell-supporting structure, they have been extensively used for that purpose in my experimentation.

A convenient way of constructing the combination of the silicate shell and its supporting structure is to bring the silicate material, in molten form, into contact with the inner walls of a relatively cool ingot mold, thereby chilling the portion of the ilicate material which is adjacent to the wall and causing it to solidify and form a shell of substantial thickness. That part of the silicate material which does not solidify in this step may be poured oil, or drained off through a suitably placed tap-hole, or it may be allowed to remain in the mold. If the excess material remains until the metal is poured, it will be displaced by the latter and rise and overflow at the top of the mold. If molten silicate material is present when the metal is poured, its temperature must be so high that the metal will not be unduly chilled, and its consistency must be such that it will extricate itself and separate completely from the metal. In any event its temperature must be above the freezing point of the metal. It is of course contemplated that the density (specific gravity) of the silicate material shall be less than that of the metal with which it is used.

In the accompanying drawing, the upper portion of the single figure shows, at a magnification of two diameters, the type of ingot surface which, under favorable conditions, is obtained by casting an 18-8 stainless steel against the bare wall of a cast iron ingot mold. The lower portion shows a typical surface obtained when the same steel is cast in a shell of silicate material in accordance with the invention.

The ensuing description has particular reference to the method of forming shells by chilling molten silicate material on the walls of an ingot mold or equivalent receptacle; but it will be clearly understood that this is only an example of the many ways in which an acceptacle shell can be made.

The molten silicate material can be brought into contact with the mold wall in various ways. Thus the material may be fused in a suitable receptacle and poured into the mold to fill the latter completely, or the mold may be partially filled with the molten material and the metal poured in upon it so that the rising layer of supernatant silicate material will form a shell on successive zones of the mold wall. Heat evolved by exothermic chemical reaction, uch as those between aluminum or silicon and energetic oxidizing agents, can be utilized under some conditions, either within or outside the mold, to raise the temperature of the silicate material, in which case the non-volatile products of the exothermic reaction will normally become assimilated with the silicate material. When such an exothermic reaction is employed, it should be caused to complete itself before the molten metal is poured into the mold. Sodium nitrate, a common oxidizing agent in exothermic mixtures, may give rise to a copious evolution of nitrogen and/ or oxides of nitrogen, and if such evolution occurs in the presence of the molten metal, it agitates the latter and prevents the formation of the desirable smooth, continuous surface on the ingot. Sodium chlorate when used as an oxidizer is reduced to products, chiefly sodium chloride, which vaporize at the high temperatures involved, and similarly bring about deleterious agitation in the solidifying metal.

As has been mentioned, any molten silicate material which is in the mold when the metal is poured must be safely above the freezing point of the metal in order that a sound ingot may be produced. This is a matter of prime importance when the excess material is not removed before the metal is cast, because heat loss from the material is rapid at the temperatures involved, and the pouring of the metal is necessarily delayed for at least a short interval to give time for the necessary operations. It may therefore be desirable to have the silicate material initially at a temperature considerably above the freezing point of the metal. Where, however, the excess liquid silicate material is removed before the metal is poured, the difiiculty just referred to is obviated.

Heat can be advantageously added to the silicate material while in the mold by employing electrical heating. This expedient is especially useful when, through some mischance, the material has become unduly cooled.

When the shell of silicate material required by the invention is produced by the method just referred to, i. e. by chilling molten material on the walls of a receptacle similar to a conventional ingot mold, it will be apparent that such a shell is not automatically formed under all conditions when the molten silicate material is brought into contact with the Wall. The case is analogous to that where a solid surface having a temperature below the freezing point of water is brought into contact with liquid water: a thick shell of ice may form on the surface, or a thin shell, or no ice at all, depending on the elapsed time, the several temperatures involved, the presence or absence of agitation, and other factors. The nature of the manipulations required to produce a suitable shell of silicate material having the characteristics hereinafter to be described will, in view of the present description, be suificiently clear to those skilled in the'art.

In order that it may not be penetrated by the molten metal, the shell of silicate material should have substantial thickness. When an ingot cast in a silicate shell supported by an ingot mold is removed from the mold, the shell normally adheres to the ingot, but is readily removed therefrom. It is found to be of considerable thickness, for example from one-thirty-second to threeeighths of an inch. In many cases the thickness is about one-sixteenth of an inch, although it ordinarily varies at different points on the same ingot. An excessively thick shell results in a small ingot and serves no useful purpose. Also, it may interfere with the removal of the ingot from the mold. Inasmuch as a portion, but not all, of the silicate shell will be melted by the introduction of the molten metal, the shell should 1 aeansaa always be of smaller internal cross section than the external cross section desired in the final ingot.

It has heretofore been proposed to cast metals into molds containing molten flux materials, but the objectives and results were not those discussed herein. In one such proposal, the object was to refine and purify the metal; and to intensify the refining action it is stated that a boiling mass of metal is treated with a slag to cause effective and repeatedly renewed contact between metal and slag. Exothermic mixtures are disclosed, and there are repeated allusions to igniting such mixtures by the first increment of metal poured. This obvious would give rise to maximum agitation of the molten metal by the evolved gases, but such agitation, desirable in a metal-refining process, is altogether undesirable in the hereindescribecl process for reasons already pointed out. Moreover, the proposal under discussion recommends materials such as strongly oxidizing slags containing a high proportion of tricalcium ferrite which, however useful they may be in refining operations, are clearly unsuitable where the objective is to produce ingots of welldeoxidized metal having smooth, unmarred surfaces.

In order to obtain the desired surface characteristics on the cast ingots it has been found to be necessary to have the molten metal to be cast in a highly refined and purified condition i. e. of the quality desired in the final material. The metal should. be fully refined to its final required. state of purity and thus, without further refinement when cast according to the process of the invention, be in a condition to be rolled, forged, pressed or otherwise worked to the desired form. The silicate material employed in the method of the invention must be substantially inert chemically toward the metallic components of the molten metal to be cast and to the supporting structure. Moreover the molten metal at the time of casting must be substantially free from inclusions or other matter which would react with the silicate material or adversely affect the surface or quality of the final product. Accordingly, in the method of the invention it is preferable to cast the molten metal directly into the silicate shell thus avoiding unnecessary agitation and mixture of the silicate material and the molten metal with possible slag entrapment. However, if proper case is employed in accordance with the teachings of this invention the molten metal may be cast into the silicate shell through a body of molten silicate material without harmful results.

This latter procedure is one means of lengthening the time interval between the preparation of the silicate shell and the casting of the ingot.

The invention has been used in the casting of workable ingots from a variety of alloy steels, and also from alloys containing only a minor proportion of iron. The method of the invention has been found to be particularly effective with alloys containing in the aggregate at least 3 of the elements chromium, molybdenum, nickel and vanadium as well as those having a chromium content of at least 10%. Good results have also been obtained from metals from which it is unusually difiicult to cast ingots having acceptable surfaces. The following may be mentioned:

S. A. E. 2320 steels containing 3.5% of nickel and 0.20% of carbon.

Chromium-nickel stainless steels of the. 18-8, 25-12 and 25-20 types.

Nickel-free chrome steels (rustless irons) con- 6 taining 17% of chromium, or chromium within the range 11% to 14%.

Acid-resistant alloys of such analysis as: Ni 64.6%, Mo 28.7%, Fe 4.9%, V 3.8%, C 0.002%.

Acid-resistant alloys of such analysis as: Ni 55.8%, Mo 16.8%, Cr 16.4%, W 3.86%, Fe 5.1%, C 0.5%.

The steels mentioned above have melting points within the approximate range 1400" C. to 1500 0., those with considerable percentages of both nickel and chromium having the lower melting points. The chromium-free non-ferrous alloys referred to have melting points in the range 1320 C. to

- 1350 C., while the melting points of the chromium-containing non-ferrous alloys (Hastelloy C) lie between 1270 C. and 1305 C. Thus the metals with which the invention is principally concerned all have melting points above 1200 C., and not substantially higher than 1500 C.

A wide variety of metallic silicates have been used in the shell-forming operation. The majority of these were calcium-magnesium-aluminum silicates, but other silicates, and particularly sodium silicate, have also been investigated. Titanium oxide has been successfully substituted for a substantial part of the silica in a composition consisting mainly of calcium oxide, magnesia and silica. The indication is that titania is the functional equivalent of silica in these compositions. In many cases fiuorspar (calcium fluoride) was added to enhance the fluidity of the metallic silicate material at the metal pouring temperature. The Ca Mg Al silicates in Examples I through V of the following table gave excellent results, as did. also the metallic silicates of Examples VI and VII. A high MnO content as shown in Example VII while suitable for use in the casting of many steels has not, in general, been found to produce satisfactory surfaces on steels containing a high percentage of chromium. Such high manganese containing silicate materials are not inert toward high chromium steels.

can ..l 10. 0

A sodium silicate composition which gave very good ingots contained NazO 31.9%; S102 63.5%.

As will be apparent. the ratio of bases to acids in these metallic silicates varies through a considerable range. This ratio is often called the basic ratio, and for the purposes of this application it is the ratio of the total moles of bases (e. g. CaO, MgO and NazO) to the moles of silica present, alumina and calcium fluoride being disregarded. Good ingots have been made where the basic ratio, so calculated, was as low as 0.5 or as high as 1.5. and. with proper precautions ratios as low as 0.3 or as high as about 2.00 are permissible. Compositions in which the basic constituent consists principally of one or more alkaline earths (magnesium, barius, calcium and strontium) and which have a basic ratio no lower than 0.8 are preferred because they have lower viscosity over a Wider range of temperatures than the more acid silicates. It will be apparent that the melting point and viscosity of the metallic silicate material can also be Varied by changing the relative proportions of the various bases even while retaining the basic ratio unaltered. Furthermore, adjustment may be made in melting point and viscosity by adding alumina and calcium fluoride. With these preferred materials, the viscosity may lie below poises at 1200 C. when the pouring temperature of the metal is about 1450 C. At higher metal pouring temperatures, for example, about 1480 C. to 1500 C. it has been found that a metallic silicate viscosity of 25 poises at 1300" C. is satisfactory and at still higher metal pouring temperatures of about 1510 C. to 1525 C., a metallic silicate viscosity of 25 poises at 1400 C. is suitable.

Metallic silicates having lower basic ratios tend to increase markedly in viscosity as the temperature falls, and become too pasty for good operation if permitted to cool very far. The sodium silicate referred to above, and glasses in general, exhibit this behavior. They pour sluggishly unless very hot, and tend to form shells of excessive thickness. Also, as the basic ratio falls, silicates lose electrical conductivity, so that they cannot be conveniently melted in an arc furnace, which is a preferred means for fusing them. However, silicates of low basic ratio often produce ingots with excellent surface characteristics.

Although several of the silicate materials given by way of example contain both calcium and magnesium, and this combination is both technically and economically satisfactory, there are many operative compositions in which one or both of these bases are replaced by alkali metals, as in the sodium silicate cited, or by other metals. The requisite properties of the silicate material are non-volatility at the metal-pouring temperature, sufficient fluidity at the metal-freezing temperature, ability to form a continuous shell on the mold wall under the herein-described conditions when an ingot mold or the like is used as a supporting envelope, absence of deleterious action on the metal of the ingot and on the supporting structure, and such stability at the casting temperature that gases are not evolved in suflicient quantity to preclude a quiescent ingot shell interface capable of producing, on cooling, an unbroken ingot surface. These properties can be obtained with silicates having a wide variety of basic constituents. To minimize agitation of the metal as it cools, continuing chemical reactions within the shell-forming material should be avoided, and the silicate material should be as nearly as possible homogeneous in composition before the metal is poured.

In the casting of ingots as heretofore practiced it is frequently uneconomical to pour the metal at temperatures as high as otherwise would be desirable because of the damage to the molds which would result therefrom. When an ingot mold is provided with a protective shell, as in the preferred embodiment of the hereindescribed method, this difficulty is obviated, and the temperature of the metal can be raised to its optimum value. This is of importance because at higher refining temperatures the metal tends more easily to free itself from objectionable inclusions. Under conventional practice when it was desirable to employ higher than normal temperatures in the melting and refining operations it was necessary to have a holding period during which the metal was allowed to cool to a suitable casting temperature before casting to avoid mold damage. With the method of the invention, however, this cooling period may be greatly shortened and in many instances dispensed with altogether. Similarly, it is often desirable to preheat the molds to higher temperatures than those now commonly used. Preheating is usually limited in order that chilling of the molten metal may occur more quickly and thereby minimize damage to the mold. A protective shell of expendable material on the mold removes this limitation, and permits the mold to be safely preheated to the desired temperature. A preheat to at least C. is desirable.

When the silicate material is prepared in a receptacle other than the mold, its temperature should ordinarily be at least 1500 C. when it is transferred to the mold, and if it is heated in the mold, as by an exothermic reaction, it should be brought to a similarly high temperature. This insures that, after the cooling which inevitably occurs before the metal is poured, the material will still be well above the freezing point of the metal at that time. To the same end, the metal should be poured as promptly as possible after the molten silicate material attains its maximum temperature in the mold: for example, with 400 pound ingots it is preferred that this interval be not more than two minutes.

In the appended claims, the term shell is intended to refer to a wall of silicate material, as hereinbefore described, against which any substantial portion of an ingot surface is formed. The invention is useful even when applied to only a part of the ingot surface. Also, envelope means any supporting or backing-up structure, whether concave, convex or substantially flat.

This application is in part a continuation of Serial No. 48,356, filed September 9, 1948, now abandoned.

What is claimed is:

1. Process of casting high melting workable metals to form a body thereof having a surface suitable for working by forging, rolling, drawing,

or the like Without surface treatment of said body for removal of surface imperfections which deleteriously affect the worked articles formed from said metals, which process comprises preparing a bath of molten metallic silicate material inert to said metal to be cast, said silicate material being further characterized in that its melting point is below that of said metal; intimately contacting the inner Walls of a casting form with said molten bath of silicate material; chilling said molten silicate material in contact with said inner walls of said casting form to form a shell reinforced by said casting form; maintaining the inner walls of said shell at a temperature in excess of the outer walls thereof; and pouring into said shell a refined and purified molten mass of said workable metal at a temperature above the melting point of said shell and at a rate such that a portion of the inner walls of said shell are melted and a surface skin of frozen metal forms within the remaining portions of said shell without contact with the inner walls of said casting form.

2. Process of casting high melting workable metals to form a body thereof having a surface suitable for Working by forging, rolling, drawing, or the like without surface treatment of said body for removal of surface imperfections which deleteriously affect the worked articles formed from said metals, which process comprises preparing a bath of molten metallic silicate material inert to said metal to be cast, said silicate material being further characterized in that its melting point is below that of said metal and in that the base to acid ratio of the constituents of said silicate material is between 0.3 and about 2.0; intimately contacting the inner walls of a casting form with said molten bath of silicate material; chilling said molten silicate material in contact with said inner walls of said casting form to form a shell reinforced by said casting form; maintaining the inner walls of said shell at a temperature in excess of the outer walls thereof; and pouring into said shell a refined and purified molten mass of said workable metal at a temperature above the melting point of said shell and at a rate such that a portion of the inner walls of said shell are melted and a surface skin of frozen metal forms within the remaining portions of said shell without contact with the inner walls of said casting form.

3. Process of casting high melting workable metals to form a body thereof having a surface suitable for working by forging, rolling, drawing, of the like without surface treatment of said body for removal of surface imperfections which deleteriously affect the worked articles formed from said metals, which process comprises preparing a bath of molten metallic silicate material inert to said metal to be cast, said silicate material being further characterized in that its melting point is below that of said metal, the principal basic constituents of said silicate material being metals of the group consisting of calcium, magnesium and manganese; intimately contacting the inner walls of a casting form with said molten bath of silicate material; chilling said molten silicate material in contact with said inner walls of said casting form to form a shell reinforced by said casting form; maintaining the inner walls of said shell at a temperature in excess of the outer walls thereof; and pouring into said shell a refined and purified molten mass of said workable metal at a temperature above the melting point of said shell and at a rate such that a portion of the inner walls of said shell are melted and a surface skin of frozen metal forms within the remaining portions of said shell without con tact with the inner walls of said casting form.

4. Process of casting high melting workable metals to form a body thereof having a surface suitable for working by forging, rolling, drawing, or the like without surface treatment of said body for removal of surface imperfections which deleteriously affect the worked articles formed from said metals, which process comprises preparing a bath of molten metallic silicate material inert to said metal to be cast; said silicate material being further characterized in that its melting point is below that of said metal and in that the base to acid ratio of the constituents of said silicate material is between 0.3 and about 2.0, the principal basic constituents of said silicate material being metals of the group consisting of calcium, magnesium and manganese; intimately contacting the inner walls of a casting form with said molten bath of silicate material; chilling said molten silicate material in contact with said inner walls of said casting form to form a shell reinforced by said casting form; maintaining the inner walls of said shell at a temperature in excess of the outer walls thereof; and pouring into said shell a refined and purified molten mass of said workable metal at a temperature above the melting point of said shell and at a rate such that a portion of the inner walls of said shell are melted and a surface skin of frozen metal forms within the remaining portions of said shell without contact with the inner walls of said casting form.

5. Process of casting high melting workable metals to form a body thereof having a surface suitable for working by forging, rolling, drawing, or the like without surface treatment of said body for removal of surface imperfections which deleteriously affect the worked articles formed from said metals which process comprises preparing a bath of molten metallic silicate material inert to said metal to be cast, said silicate material being further characterized in that it is fluid at 1500 C. and in that its melting point is below that of said metal; intimately contacting the inner walls of a casting form with said molten bath of silicate material; chilling said molten silicate material in contact with said inner walls of said casting form to form a shell reinforced by said casting form; maintaining the inner walls of said shell at a temperature in excess of the outer walls thereof; and pouring into said shell a refined and purified mass of said workable metal at a temperature above the melting point of said shell and at a rate such that a portion of the inner walls of said shell are melted and a surface skin of frozen metal forms within the remaining portions of said shell without contact with the inner walls of said casting form.

6. Process of casting steel to form a body therof having a surface suitable for working by forging, rolling, drawing, or the like without surface treatment of said body for removal of surface imperfections which deleteriously affect the worked articles formed from said steel, which process comprises preparing a bath of molten metallic silicate material inert to said steel to be cast, said silicate material being further characterized in that its melting point is below that of said steel and in that the base to acid ratio of the constituents of said silicate material is between 0.3 and about 2.0; intimately contacting the inner walls of a casting form with said molten bath of silicate material; chilling said molten silicate material in contact with said inner walls of said casting form to form a shell reinforced by said casting form; maintaining the inner walls of said shell at a temperature in excess of the outer walls thereof; and pouring into said shell a refined and purified molten mass of said steel at a temperature above the melting point of said shell and at a rate such that a portion of the inner walls of said shell are melted and a surface skin of frozen steel forms within the remaining portions of said shell without contact with the inner walls of said casting form.

7. Process of casting stainless steel to form a body thereof having a surface suitable for work ing by forging, rolling, drawing, or the like Without surface treatment of said body for removal of surface imperfections which deleteriously affect the Worked articles formed from said stainless steel, which process comprises preparing a bath of molten metallic silicate material inert to said stainless steel to be cast, said silicate material being further characterized in that its melting point is below that of said stainless steel and in that the base to acid ratio of the constituents of said silicate material is between 0.5 and 1.5; intimately contacting the inner walls of a casting form with said molten bath of silicate material; chilling said molten silicate material in contact with said inner walls of said casting form to form a shell reinforced by said casting form; maintaining the inner walls of said shell at a temperature in excess of the outer walls thereof; and pouring into said shell a refined and purified molten mass of said stainless steel at a temperature above the melting point of said shell and at a rate such that a portion of the inner walls of said shell are melted and a surface skin of frozen stainless steel forms within the remaining portions of said shell without contact 5 with the inner walls of said casting form.

HARRY E. KENNEDY.

REFERENCES CITED The following references are of record in the 10 file of this patent:

UNITED STATES PATENTS Number Name Date 852,671 McArthur May 7, 1907 15 Number Number Name Date Monnot Aug. 3, 1909 De Witt July 15, 1930 Freed Aug. 4, 1931 Hall Aug. 15, 1939 Moore Nov. 26, 1940 Anderson Dec. 8, 1942 York Dec. 11, 1945 Dunn et a1. Jan. 3, 1950 FOREIGN PATENTS Country Date, Great Britain Nov. 14, 1929 Great Britain Apr. 14, 1936 Germany May 31, 1938 

1. PROCESS OF CASTING HIGH MELTING WORKABLE METALS TO FORM A BODY THEREOF HAVING A SURFACE SUITABLE FOR WORKING BY FORGING, ROLLING, DRAWING, OR THE LIKE WITHOUT SURFACE TREATMENT OF SAID BODY FOR REMOVAL OF SURFACE IMPERFECTIONS WHICH DELETERIOUSLY AFFECT THE WORKED ARTICLES FORMED FROM SAID METALS, WHICH PROCESS COMPRISES PREPARING A BATH OF MOLTEN METALLIC SILICATE MATERIAL INERT TO SAID METAL TO BE CAST, SAID SILICATE MATERIAL BEING FURTHER CHARACTERIZED IN THAT ITS MELTING POINT IS BELOW THAT OF SAID METAL; INTIMATELY CONTACTING THE INNER WALLS OF A CASTING FORM WITH SAID MOLTEN BATH OF SILICATE MATERIAL; CHILLING SAID MOLTEN SILICATE MATERIAL IN CONTACT WITH SAID INNER WALLS OF SAID CASTING FORM TO FORM A SHELL REINFORCED BY SAID CASTING FORM; MAINTAINING THE INNER WALLS OF SAID SHELL AT A TEMPERATURE IN EXCESS OF THE OUTER WALLS THEREOF; AND POURING INTO SAID SHELL A REFINED AND PURIFIED MOLTEN MASS OF SAID WORKABLE METAL AT A TEMPERATURE ABOVE THE MELTING POINT OF SAID SHELL AND AT A RATE SUCH THAT A PORTION OF THE INNER WALLS OF SAID SHELL ARE MELTED AND A SURFACE SKIN OF FROZEN METAL FORMS WITHIN THE REMAINING PORTIONS OF SAID SHELL WITHOUT CONTACT WITH THE INNER WALLS OF SAID CASTING FORM. 